258 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



and brackish, and in this respect resembles all streams flowing among 

 gypsum-deposits . 



From the above facts it may be presumed, although positive 

 sections are vt^anting, that the gypsum formation passes beneath the 

 basin of the Tigris and Euphrates, — that it rises to the surface, in 

 low rounded patches or elongated ridges, at certain localities between 

 those rivers, — and that it reappears in the deserts to the west of the 

 Euphrates. 



The difficulty of obtaining sections in the deserts is unfortunate, 

 because I am unable to state with certainty the exact position of the 

 gravels, sands, and gypsum-beds of the above localities with respect 

 to the well-defined sections on the verge of the mountains. 



It is worthy of remark, that I have nowhere but in the plains of 

 the great rivers observed gypsum immediately overlaid by quartz- 

 and chert-gravel. It is therefore possible that these deposits are 

 subsequent to the sands and gravels of the Hamrine Hills and the 

 gypsum-beds further to the east. 



Section (fig. 2) from Baghdad to Zohdb. — In passing from Baghdad 

 along the great caravan-road into Persia, by way of Khanikin 

 and Kasri Shirin (see fig. 2), we have a constant appearance of 

 cherty and quartzose gravel-beds of the same character as those at 

 Iskenderia. 



From Baghdad to Shehrebau (48 miles) is a perfectly level desert ; 

 but between the latter place and Kisil Robat the road crosses the 

 low range of the Hamrine Hills. These consist of reddish, yellow, 

 coarse, calcareous sandstones and loose gravels, alternating with red 

 sandy marls ; the whole series has a gentle dip to the N.E., and is 

 covered by the gravel detached from its original bed. 



Between Kisil Robat and Khanikin there intervenes a still higher 

 range of precisely similar composition, the beds of which have the 

 same dip towards the N.E. 



The elevation of these ranges appears to be due to lateral pres- 

 sure ; and faults no doubt exist beneath the alluvial sandy plains of 

 Kisil Robat and Khanikin, whereby the continuity of the beds is 

 broken. 



These reappear to the N.E. of Khanikin, and run without inter- 

 mission to Kasr-i-Shirin (fig. 2). The peculiar character of the 

 sandstone-portion of the gy|)sum-series now begins to show itself. 

 It consists of low tabular hills, when the stratification is nearly hori- 

 zontal ; the red chert-gravel towards the S.W. forming cappings, but 

 alternating with a succession of friable red sandstones and marls. 

 Proceeding eastward, the marls predominate over the sandstones ; 

 and the beds, which previously appear dipping one way and then 

 another, take a S.W. direction on approaching Kasr-i-Shirin, and 

 present a succession of little escarpments towards the village. At 

 this place the sandstones and underlying marls rest conformably, at 

 an angle of about 1 5°, on the high ridges of pure gypsum which ter- 

 minate the N.W. extremity of the limestone-range of hills called 

 Sumbiilah. 



